<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>菜鸟教程(runoob.com)</title>
<style>
    ul
    {
    list-style-type:none;
    padding:0;margin:0;
    width:200px;
    background-color:#f1f1f1;
    }
    li a
    {
    display:block;
    color:green;
    padding:16px ;
    text-decoration;none;
    }
    <!--/* 鼠标移动到选项上修改背景颜色 */-->
    li a:hover
    {
    background-color:green;
    color:white;
    }
    .dropdown {
    position: relative;
    display: inline-block;
    }

    .dropdown-content {
        display: none;
        position: absolute;
        background-color: #f9f9f9;
        min-width: 200px;
        box-shadow: 8px 8px 16px 8px rgba(0,0,0,0.2);
    }

    .dropdown-content a {
        color: black;
        padding: 24px 32px;
        text-decoration: none;
        display: block;
    }

    .dropdown-content a:hover {background-color: green}

    .dropdown:hover .dropdown-content {
        display: block;
    }

    .dropdown:hover .dropbtn {
        background-color: green;
    }
</style>
</head>
<body>
<ul>
    <li><a href="https://www.wjx.cn/jq/25598173.aspx">一级栏目</a></li>
    <div class="dropdown">
    <a href="#" class="dropbtn">二级栏目</a>
    <div class="dropdown-content">
      <a href="#">链接 1</a>
      <a href="#">链接 2</a>
      <a href="#">链接 3</a>
    </div>
  </div>
</ul>

</body>
</html>